This invention is particularly adapted to ribbon drives for impact printers. Such impact printers can be dot matrix printers and more specifically line type printers. Such line printers are known in the art and have been developed extensively by the assignee of this invention.
The inked ribbons of such various printers are repeatedly impacted against a length of print paper or other printable medium by certain impact elements. The impact elements can each define a shape or a character or simply print dots, with characters or other indicia to be printed being formed in a dot matrix fashion.
Such dot matrix printers can be of the line printer type in which a plurality of hammers or other impact printing mechanisms are mounted along the length of a hammerbank. They are driven by a shuttle assembly and are selectively actuated to impact the print paper. The impact is through a length of inked ribbon. This prints dots on the paper as the shuttle assembly is caused to undergo reciprocating motion relative to the paper.
The inked ribbon extends through the print station and has the opposite ends thereof wound upon an opposite pair of spools. During printing, the opposite spools of the ribbon drive are rotatably driven to provide continuous motion of the length of ribbon through the print station. When the end of the ribbon is reached the direction of drive of the spools is reversed. This causes the ribbon to move through the print station in the opposite direction.
A pair of two phase stepper motors control the tension and the velocity of the print ribbon between two spools. At any given time during printing, one motor pulls ribbon through the print station at a substantial constant velocity while the second motor is run in a regenerative mode to provide tension. When the ribbon reaches the end of it's travel in any given direction, it's direction is reversed so that the function of the two respective motors and spools are then reversed.
The angular velocity of the feed motor or motor attached to the spool from which the ribbon is unwinding, is calculated by counting the number of zero crossings on the back EMF waveform. In any given period of time the angular velocity of the take-up motor is set by the system micro controller. The ratio of the angular velocities of the feed take-up spool or reel is a unique number over the range of ribbon radii in the system. The radius of the ribbon material on each reel can be determined at set intervals based upon the ratio of the angular velocities. This ratio information used to determine the angular velocity and tension is updated at any given time.
A major problem with regard to loading the inked ribbon into a printer is the fact that the ribbon itself has ink which can be imparted to any surface which it touches. This is particularly true with regard to a user's hands. When handling the ribbon, users often times find their hands very dirty as well as various portions of the equipment.
In the past, it has been a significant problem to load an inked ribbon without getting dirty. When loading the ribbon, it is also necessary to determine where the actual clean portion and the inked portion is.
In the past, there have been attempts to provide clean ribbons by having non-inked strips of various material. However, there has been no ability to effect the loading of the strip and have a fail safe means of recognizing the position of where the clean strip is in comparison to the inked ribbon.
The invention hereof provides for a printer ribbon having a clean hands portion formed of an electrically conductive plastic or other material that can be monitored with respect to the interface at which it is connected to the inked portion of the ribbon. This allows a user and installer of the ribbon to emplace the ribbon by merely handling the non-inked portions and emplacing it over the spools or spindles which are driven by the motors. Thereafter, the system of this invention detects where the non-inked portion is and determines at a particular juncture or interface of the non-inked portion and the inked portion when and where printing can begin.
The foregoing is effectuated through the circuitry of this invention and in particular the detection of the respective angular velocity of one spool compared to the other.
An object of this invention is to permit the loading of an inked ribbon into a printer without smudging or soiling a user or the surrounding area in which the ribbon is loaded.
Another object of this invention is to allow for a clean type of ribbon leader to be emplaced in a printer on a relatively automated basis.
A further object of this invention is to allow a print ribbon to be emplaced within a printer and not create a soiling condition for an operator while at the same time allowing an operator to avoid having to handle the ribbon after it has been emplaced for positioning with respect to the printing functions.
Another object of this invention is to automatically detect a position of a clean ribbon leader with respect to the inked print ribbon so that printing can commence with respect to the inked ribbon portions on an automated basis.
An important final object of this invention is to allow a print ribbon to be emplaced in a printer with clean leaders extending therefrom and a detection of the position of the clean leaders to effect automated startup of printing functions after emplacement of the ribbon in the printer.